From 34dc27f02cb3799d56a99002261e4d091da0cea4 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 5 Nov 2025 12:32:02 -0800 Subject: srcu: Create an srcu_expedite_current() function This commit creates an srcu_expedite_current() function that expedites the current (and possibly the next) SRCU grace period for the specified srcu_struct structure. This functionality will be inherited by RCU Tasks Trace courtesy of its mapping to SRCU fast. If the current SRCU grace period is already waiting, that wait will complete before the expediting takes effect. If there is no SRCU grace period in flight, this function might well create one. [ paulmck: Apply Zqiang feedback for PREEMPT_RT use. ] Signed-off-by: Paul E. McKenney Cc: Andrii Nakryiko Cc: Alexei Starovoitov Cc: Peter Zijlstra Cc: Signed-off-by: Frederic Weisbecker --- include/linux/srcutree.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'include/linux/srcutree.h') diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 42098e0fa0b7..93ad18acd6d0 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -42,6 +42,8 @@ struct srcu_data { struct timer_list delay_work; /* Delay for CB invoking */ struct work_struct work; /* Context for CB invoking. */ struct rcu_head srcu_barrier_head; /* For srcu_barrier() use. */ + struct rcu_head srcu_ec_head; /* For srcu_expedite_current() use. */ + int srcu_ec_state; /* State for srcu_expedite_current(). */ struct srcu_node *mynode; /* Leaf srcu_node. */ unsigned long grpmask; /* Mask for leaf srcu_node */ /* ->srcu_data_have_cbs[]. */ @@ -135,6 +137,11 @@ struct srcu_struct { #define SRCU_STATE_SCAN1 1 #define SRCU_STATE_SCAN2 2 +/* Values for srcu_expedite_current() state (->srcu_ec_state). */ +#define SRCU_EC_IDLE 0 +#define SRCU_EC_PENDING 1 +#define SRCU_EC_REPOST 2 + /* * Values for initializing gp sequence fields. Higher values allow wrap arounds to * occur earlier. @@ -210,6 +217,7 @@ struct srcu_struct { int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp); void synchronize_srcu_expedited(struct srcu_struct *ssp); void srcu_barrier(struct srcu_struct *ssp); +void srcu_expedite_current(struct srcu_struct *ssp); void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf); // Converts a per-CPU pointer to an ->srcu_ctrs[] array element to that -- cgit v1.2.3 From ee90848499b169070dbf85a4276a45ccbb7ff7d3 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 5 Nov 2025 12:32:04 -0800 Subject: srcu: Create a DEFINE_SRCU_FAST() This commit creates DEFINE_SRCU_FAST() and DEFINE_STATIC_SRCU_FAST() macros that are similar to DEFINE_SRCU() and DEFINE_STATIC_SRCU(), but which create srcu_struct structures that are usable only by readers initiated by srcu_read_lock_fast() and friends. This commit does make DEFINE_SRCU_FAST() available to modules, in which case the per-CPU srcu_data structures are not created at compile time, but rather at module-load time. This means that the >srcu_reader_flavor field of the srcu_data structure is not available. Therefore, this commit instead creates an ->srcu_reader_flavor field in the srcu_struct structure, adds arguments to the DEFINE_SRCU()-related macros to initialize this new field, and extends the checks in the __srcu_check_read_flavor() function to include this new field. This commit also allows dynamically allocated srcu_struct structure to be marked for SRCU-fast readers. It does so by defining a new init_srcu_struct_fast() function that marks the specified srcu_struct structure for use by srcu_read_lock_fast() and friends. Signed-off-by: Paul E. McKenney Cc: Mathieu Desnoyers Cc: Steven Rostedt Cc: Sebastian Andrzej Siewior Cc: Signed-off-by: Frederic Weisbecker --- include/linux/srcutree.h | 30 +++++++++++++++++++----------- 1 file changed, 19 insertions(+), 11 deletions(-) (limited to 'include/linux/srcutree.h') diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 93ad18acd6d0..7ff4a11bc5a3 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -104,6 +104,7 @@ struct srcu_usage { struct srcu_struct { struct srcu_ctr __percpu *srcu_ctrp; struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */ + u8 srcu_reader_flavor; struct lockdep_map dep_map; struct srcu_usage *srcu_sup; /* Update-side data. */ }; @@ -162,20 +163,21 @@ struct srcu_struct { .work = __DELAYED_WORK_INITIALIZER(name.work, NULL, 0), \ } -#define __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ +#define __SRCU_STRUCT_INIT_COMMON(name, usage_name, fast) \ .srcu_sup = &usage_name, \ + .srcu_reader_flavor = fast, \ __SRCU_DEP_MAP_INIT(name) -#define __SRCU_STRUCT_INIT_MODULE(name, usage_name) \ +#define __SRCU_STRUCT_INIT_MODULE(name, usage_name, fast) \ { \ - __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ + __SRCU_STRUCT_INIT_COMMON(name, usage_name, fast) \ } -#define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name) \ +#define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name, fast) \ { \ .sda = &pcpu_name, \ .srcu_ctrp = &pcpu_name.srcu_ctrs[0], \ - __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ + __SRCU_STRUCT_INIT_COMMON(name, usage_name, fast) \ } /* @@ -196,23 +198,29 @@ struct srcu_struct { * init_srcu_struct(&my_srcu); * * See include/linux/percpu-defs.h for the rules on per-CPU variables. + * + * DEFINE_SRCU_FAST() creates an srcu_struct and associated structures + * whose readers must be of the SRCU-fast variety. */ #ifdef MODULE -# define __DEFINE_SRCU(name, is_static) \ +# define __DEFINE_SRCU(name, fast, is_static) \ static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \ - is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage); \ + is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage, \ + fast); \ extern struct srcu_struct * const __srcu_struct_##name; \ struct srcu_struct * const __srcu_struct_##name \ __section("___srcu_struct_ptrs") = &name #else -# define __DEFINE_SRCU(name, is_static) \ +# define __DEFINE_SRCU(name, fast, is_static) \ static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data); \ static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \ is_static struct srcu_struct name = \ - __SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data) + __SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data, fast) #endif -#define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */) -#define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static) +#define DEFINE_SRCU(name) __DEFINE_SRCU(name, 0, /* not static */) +#define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, 0, static) +#define DEFINE_SRCU_FAST(name) __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST, /* not static */) +#define DEFINE_STATIC_SRCU_FAST(name) __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST, static) int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp); void synchronize_srcu_expedited(struct srcu_struct *ssp); -- cgit v1.2.3 From ac51c40c2c148a75f3191ff401c9889a7fc12cb1 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 5 Nov 2025 12:32:08 -0800 Subject: srcu: Make SRCU-fast readers enforce use of SRCU-fast definition/init This commit makes CONFIG_PROVE_RCU=y kernels enforce the new rule that srcu_struct structures that are passed to srcu_read_lock_fast() and other SRCU-fast read-side markers be either initialized with init_srcu_struct_fast() on the one hand or defined with DEFINE_SRCU_FAST() or DEFINE_STATIC_SRCU_FAST() on the other. This eliminates the read-side test that was formerly included in srcu_read_lock_fast() and friends, speeding these primitives up by about 25% (admittedly only about half of a nanosecond, but when tracing on fastpaths...) Signed-off-by: Paul E. McKenney Cc: Mathieu Desnoyers Cc: Steven Rostedt Cc: Sebastian Andrzej Siewior Cc: Signed-off-by: Frederic Weisbecker --- include/linux/srcutree.h | 16 +--------------- 1 file changed, 1 insertion(+), 15 deletions(-) (limited to 'include/linux/srcutree.h') diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 7ff4a11bc5a3..6080a9094618 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -307,21 +307,7 @@ __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp) void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor); -// Record reader usage even for CONFIG_PROVE_RCU=n kernels. This is -// needed only for flavors that require grace-period smp_mb() calls to be -// promoted to synchronize_rcu(). -static inline void srcu_check_read_flavor_force(struct srcu_struct *ssp, int read_flavor) -{ - struct srcu_data *sdp = raw_cpu_ptr(ssp->sda); - - if (likely(READ_ONCE(sdp->srcu_reader_flavor) & read_flavor)) - return; - - // Note that the cmpxchg() in __srcu_check_read_flavor() is fully ordered. - __srcu_check_read_flavor(ssp, read_flavor); -} - -// Record non-_lite() usage only for CONFIG_PROVE_RCU=y kernels. +// Record SRCU-reader usage type only for CONFIG_PROVE_RCU=y kernels. static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor) { if (IS_ENABLED(CONFIG_PROVE_RCU)) -- cgit v1.2.3 From d3f52f53a56278ce5ffeafa3cc6cfb3ecef770fe Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 5 Nov 2025 12:32:14 -0800 Subject: srcu: Create an SRCU-fast-updown API This commit creates an SRCU-fast-updown API, including DEFINE_SRCU_FAST_UPDOWN(), DEFINE_STATIC_SRCU_FAST_UPDOWN(), __init_srcu_struct_fast_updown(), init_srcu_struct_fast_updown(), srcu_read_lock_fast_updown(), srcu_read_unlock_fast_updown(), __srcu_read_lock_fast_updown(), and __srcu_read_unlock_fast_updown(). These are initially identical to their SRCU-fast counterparts, but both SRCU-fast and SRCU-fast-updown will be optimized in different directions by later commits. SRCU-fast will lack any sort of srcu_down_read() and srcu_up_read() APIs, which will enable extremely efficient NMI safety. For its part, SRCU-fast-updown will not be NMI safe, which will enable reasonably efficient implementations of srcu_down_read_fast() and srcu_up_read_fast(). This API fork happens to meet two different future use cases. * SRCU-fast will become the reimplementation basis for RCU-TASK-TRACE for consolidation. Since RCU-TASK-TRACE must be NMI safe, SRCU-fast must be as well. * SRCU-fast-updown will be needed for uretprobes code in order to get rid of the read-side memory barriers while still allowing entering the reader at task level while exiting it in a timer handler. This commit also adds rcutorture tests for the new APIs. This (annoyingly) needs to be in the same commit for bisectability. With this commit, the 0x8 value tests SRCU-fast-updown. However, most SRCU-fast testing will be via the RCU Tasks Trace wrappers. [ paulmck: Apply s/0x8/0x4/ missing change per Boqun Feng feedback. ] [ paulmck: Apply Akira Yokosawa feedback. ] Signed-off-by: Paul E. McKenney Cc: Andrii Nakryiko Cc: Alexei Starovoitov Cc: Peter Zijlstra Cc: Signed-off-by: Frederic Weisbecker --- include/linux/srcutree.h | 55 ++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 53 insertions(+), 2 deletions(-) (limited to 'include/linux/srcutree.h') diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 6080a9094618..d6f978b50472 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -199,8 +199,15 @@ struct srcu_struct { * * See include/linux/percpu-defs.h for the rules on per-CPU variables. * - * DEFINE_SRCU_FAST() creates an srcu_struct and associated structures - * whose readers must be of the SRCU-fast variety. + * DEFINE_SRCU_FAST() and DEFINE_STATIC_SRCU_FAST create an srcu_struct + * and associated structures whose readers must be of the SRCU-fast variety. + * DEFINE_SRCU_FAST_UPDOWN() and DEFINE_STATIC_SRCU_FAST_UPDOWN() create + * an srcu_struct and associated structures whose readers must be of the + * SRCU-fast-updown variety. The key point (aside from error checking) with + * both varieties is that the grace periods must use synchronize_rcu() + * instead of smp_mb(), and given that the first (for example) + * srcu_read_lock_fast() might race with the first synchronize_srcu(), + * this different must be specified at initialization time. */ #ifdef MODULE # define __DEFINE_SRCU(name, fast, is_static) \ @@ -221,6 +228,10 @@ struct srcu_struct { #define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, 0, static) #define DEFINE_SRCU_FAST(name) __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST, /* not static */) #define DEFINE_STATIC_SRCU_FAST(name) __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST, static) +#define DEFINE_SRCU_FAST_UPDOWN(name) __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST_UPDOWN, \ + /* not static */) +#define DEFINE_STATIC_SRCU_FAST_UPDOWN(name) \ + __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST_UPDOWN, static) int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp); void synchronize_srcu_expedited(struct srcu_struct *ssp); @@ -305,6 +316,46 @@ __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp) atomic_long_inc(raw_cpu_ptr(&scp->srcu_unlocks)); // Z, and implicit RCU reader. } +/* + * Counts the new reader in the appropriate per-CPU element of the + * srcu_struct. Returns a pointer that must be passed to the matching + * srcu_read_unlock_fast_updown(). This type of reader is compatible + * with srcu_down_read_fast() and srcu_up_read_fast(). + * + * See the __srcu_read_lock_fast() comment for more details. + */ +static inline +struct srcu_ctr __percpu notrace *__srcu_read_lock_fast_updown(struct srcu_struct *ssp) +{ + struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp); + + if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) + this_cpu_inc(scp->srcu_locks.counter); // Y, and implicit RCU reader. + else + atomic_long_inc(raw_cpu_ptr(&scp->srcu_locks)); // Y, and implicit RCU reader. + barrier(); /* Avoid leaking the critical section. */ + return scp; +} + +/* + * Removes the count for the old reader from the appropriate + * per-CPU element of the srcu_struct. Note that this may well be a + * different CPU than that which was incremented by the corresponding + * srcu_read_lock_fast(), but it must be within the same task. + * + * Please see the __srcu_read_lock_fast() function's header comment for + * information on implicit RCU readers and NMI safety. + */ +static inline void notrace +__srcu_read_unlock_fast_updown(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp) +{ + barrier(); /* Avoid leaking the critical section. */ + if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) + this_cpu_inc(scp->srcu_unlocks.counter); // Z, and implicit RCU reader. + else + atomic_long_inc(raw_cpu_ptr(&scp->srcu_unlocks)); // Z, and implicit RCU reader. +} + void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor); // Record SRCU-reader usage type only for CONFIG_PROVE_RCU=y kernels. -- cgit v1.2.3